Natural pumice stone is of volcanic origin, is abrasive, relatively lightweight, and contains solid and gaseous components. Natural pumice is useful by millenaries for treating cloth as by softening and discoloring denim, linen, and the like, for filing, for polishing, and for many other purposes. While natural pumice stone has desirable qualities of abrasivity and relatively lightweight, it also has very inconsistent quality since the size and type of the individual stones varies widely even within the same mine, and oftentimes even within the same bag from a particular location within a mine. Also, good quality pumice stone is difficult to find since many of the prime quality mines are almost exhausted, and exploitation of other mines is limited because of the location of the mines, and/or because of environmental protection regulations. Further, natural pumice stone contains up to about 70% by weight of water which adds to shipping costs. Further, the water content often diminishes during shipping and storage, and this water content variation can adversely affect the utility of the pumice stone for cloth treating processes and the like.
Artificial pumice stones are also known. Conventional artificial pumice is typically formed from expanded ceramic or expanded concrete. Artificial pumice produced in this way typically has less than desired abrasivity, and has low mechanical strength, thus being consumed quickly.
According to the present invention, artificial pumice is provided that is made of cellular glass. Cellular glass artificial pumice is very abrasive, since the glass cell walls are sharp microscopic "knives". Also, the density, mechanical strength, cell size, and abrasivity of the cellular glass pumice is precisely regulatable during the manufacture, and thus cellular glass pumice has known quality, and the quality may be optimized for each particular situation. The cellular glass pumice according to the invention also typically is dry (unless liquid is specifically introduced therein for a particular purpose), and therefore shipping weight is minimized and quality is precisely controlled when it is desired to introduce liquid into the individual stones.
Due to its high mechanical strength and other desirable properties, one kilogram of cellular glass pumice according to the invention can be substituted for 2-10 kilograms of natural pumice, or expanded ceramic or concrete pumice, thus reducing shipping and storage costs, as well as utilization costs.
Of course cellular glass per se is known, as are methods for manufacturing cellular glass products. However most known uses for cellular glass are for thermal insulation. Such cellular glass products are regular in shape, for example being cut with saws (e.g. diamond or carborundum saws). This is in clear contra-distinction to the artificial pumice stones according to the invention which are specifically irregularly shaped with open cells that provide the needed abrasivity, and with any glass crust removed. Edges and points are also rounded since sharp edges can hurt a handler's hands, or damage materials with which the pumice cooperates in use (e.g. damage the cloth during cloth treatment).
According to the invention, artificial pumice is provided comprising cellular glass bodies devoid of glass crust and with rounded edges and points, preferably having a density between about 0.2-2.0 grams per cubic centimeter and preferably having maximum size of between about 1-30 centimeters. The cellular glass bodies may be filled with a liquid, such as water, acid, or a wide variety of textile treating liquids.
The cellular glass bodies with relatively small sizes can be obtained by two methods. The first method consists of dosing relatively small independent portions of the mixture of glass particles and cellulating agent obtaining, after the kiln process, bodies with sizes near to end sizes. The second method consists in reducing larger cellular glass bodies to smaller bodies preferably by exposing the large bodies to a sudden temperature change. This may also be accomplished mechanically by compression, flexion, impact or otherwise.
Also according to the present invention, a method is provided for producing artificial pumice. The method comprises the steps of sequentially: (a) Mixing particles selected from the group essentially of glass (e.g. waste glass particles with a maximum particle size of about 1 millimeter) and vitrifiable materials, such as sand or basalt, with a cellulating agent such as calcium or magnesium carbonate. (b) Heating the mixtures to melt the particles so as to produce relatively large cellular bodies, such as by disposing the mixture on a clay covered continuous refractory belt which continuously passes into a kiln having a temperature of about 700.degree. C. or more. (c) Reducing the size of the large cellular glass bodies to produce smaller cellular glass bodies, such as by exposing the large bodies to a sudden temperature change (e.g. cooling at a rate of between about 100-400.degree. C. per minute), or by mechanical action (e.g. punching, compression, flexion, impacting, etc.); and (d) removing any glass crust from the smaller bodies and rounding edges and points thereof by bringing the smaller bodies into abrasive contact with each other, such as by placing them in a rotary cylinder and rotating the cylinder. Preferably an alkaline silicate, or the like, is also added to the mixture to promote sticking of the granules together, and to avoid the formation of fissures in the final artificial pumice product produced. The further step (e) of filling the smaller cellular glass bodies with liquid (as by exposing them to a vacuum, and then to a liquid) may also be practiced, as may be the further step (al) --between steps (a) and (b) -- of compacting the mixture.
It is the primary object of the present invention to provide an artificial pumice with desirable properties, and a simple and effective method of production thereof. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.